ACKNOWLEDGEMENT

College, Calcutta, for his guidance during the field study in Garhbeta, Midnapore) ^1 and for his non stop motivation to carry out studies in the post field work.(His ideas, remarkable understanding of Fluvial Geomorphology and support has greatly contributed in carrying out this research work!)

am also indebted to Sri Jayanta Sen, Research Scholar of Vidyasagar

University, Midnapore West Bengal for supplying the useful maps and documents?) ^

1 am also grateful to my parents who always inspired me to carry out my

TRODUCTIONV Gully development atfV Gangani near Garhbeta, A Medinipur district, West

pr Bengal, India has given rise to a mesoscale badland

landscape. Exquisite chromatic association of land^ forms and awe-inspiring character of topography calls for investigation of geomorphic processes that have dominated the terrain in the past and are operating even today in the area.

LOCATION The Garhbeta Badlands (22° 49'N, 87° 27'E) is situated in west Medinipur district of West Bengal, India. This area is locally known as 4Ganganir Danga' (Land of Fire). The area lies on he Howrah-Adra-Chakradharpur route of the South-Eastern Railway and is located at a distance of 176kms. from Calcutta and is approachable23 by both road & railways.

v/dBJECTIVES The Specific objectives of the study are - (i) to delineate the nature and characteristics of gullies, (ii) to detect the Causes of the development of rills and gullies of the area; (Hi) to classify the gullies based on their nature and extension;

^METHODOLOGY field methods the maps and data products (digital-he imagery) have collected from different Govt. Sources. Inentire the field, extensive field work has been done in eachwork sector and phase according to the levels ofhas development for micro level study and to observe thebeen nature and delineate the morphological characteristicsperfor of the study area. In post field work the data have beenmed processed and analysed by modern Geomorphic andby analytical techniques and ultimately attempt have beendiffer taken to delineate the impact of ravine development onent surrounding.phas PREVIOUSes LITERATUREandmeth Besides depending on the fieldwork at Garhbeta,

ods other geomophological data & informations are taken

are -from different journals of Bondhopadhyay S, Jayanta

(I) Sen, Suman Sen, Kanailal Das & other's who have

Pre- done work in this area.

field;(ii)Fieldand(iii)Post-fieldmethod. InPre- sy GEOLOGIC DEVELOPMENT The region around our study area have thick mantle of lateriteoccupying the high lands along the bank of river Silai. They are believed to beof Pleistocene age. The thickness of this laterite capping varies graduallybetween 6-25 metres.

The result of exploratory boreholes in the area revealed that there is a

gradual increase in depth of the basement rock (granite gneiss) withconsequent increase in the thickness of the semi-consolidated or looselyconsolidated sediments including the laterite from west to east and southwestdirections. This view also was corroborated by the findings from thegeophysical studies in the area. The palaeontological evidence also indicateda gradual increase in the base of Pleistosene sediments from 106 to 152metres to the east (Goswami, 1964-65).

Geology of the area is concealed under a blanket of laterite and laterite

soils. Based on he critical appraisal of the lithological logs and electrical logs ofthe boreholes drilled in the area the lithological sequence works out asfollows:-

CLIMATE The climate of the study area has been identified as sub-humidmonsoon type. Hot dry summer season (March - May), wet monsoon season(June -October) and dry-cool winter (December - January) are the threeimportant seasons that cover most of the time of the year. During summer, themaximum temperature increases to 45°C or more. The bare and dark colouredlateritic surface produces maximum radiation of heat energy during this time.The area receives an average rainfall of 140cm yr"1. Dry and cool winterseason lasts about three months in a year when minimum temperature goesdown to below 9°C. The seasonal fluctuations oftemperature and humidity have a great impact on laterisation processes and

badland development over the study area.

^NATURAL VEGETATION Our study are was once covered with mixed deciduous forest and was a part of Jangal mahal of Rarh upland before independence. Sal (Shorea robusta) was the most important tree associated with Shimul (bombax ceibal), Mahua (madhuca indica), Jarul {lagerstroemia speciosa) etc. Presently, low sub-soil acidity, high subsurface calcium and absence of organic matter are indicative of poor growth and regeneration of sal. In most of the places the topsoil has been washed away which is not favourable to the ecosystem.

|: /^OIL FORMATION t

The region is characterised with loose and dry surface soil with presence of highly indurated duricrust. The sediments of the area are mostly concealed under a blanket of duricrust. As laterite is heavily leached tropical subsoil, when exposed, it dries and gets rock-like due to cementing of ferruginous concretions by iron oxide colloids (Mallick and Niyogi, 1970). It is not a fertile soil. At Garhbeta laterite also consists of aluminum oxyhydroxides with smaller amounts of iron oxyhydroxides and a little bit of a clay mineral called halloysite. Silica, calcium, magnesium, potassium and sodium are present in very low amounts of absent. Laterite formations span several kilometers on the right bank of river Silai. The topography very much resembles the Australian "breakaways" with a broad flattish and dissected top and undercut softer materials below (Mallick and Niyogi 1970, Biswas 1987). L ATERITIC PROFILE AT GARHBETA BADLANDSequence Name Slope Thickness (m) Characteristics1 Surface 3" or less 0.5 A Surficial cover of red clayey so Layer in many places, with some sand concretions.2 Laterite 5 -15° U 2.0-4.0 A layer of nodular duricrust, part duricrust containing iron concretions nodules, which are tabular & large to be called pipes often dra water, from the solutionai & co developed on the surface, indurated layer being often vertically by gullies running d river.3 Mottled Nearly 4.0-6.0 A layer of redish & sometim clay 60° mottled clay, mired with some layer as course sand, traversed in pla hardpans, cut away by rills & g scarp face.4 Palled 35° -45° 5.0 A pallied layer of yellowish zone containing very little of sand layer irregular in occurrence, pure cl only in pockets, producing on away.

We can also describe the nature of soil and sediment properties in the study

by the side Of River silatS-4 Erosional 5.5 0 62 41.8 4.9 16.3 L 401 85. laterite t • upland cultivable during wet period QUANTITATIVE ASSESSMENT OF GROWTH OF GULLIES IN

ARHBETA

Following Table gives clear indication on progress of

the badland based on estimation of authentic secondaryinformation viz. Survey of India topographical maps (1:50,000),Aerial photographs (1:60,000), satellite data (IRS LISS IIIGeocoded, 1:50,000; IRS ID PAN Image - 2001, and groundsurvey since 1995. It can be seen that the affected area hasincreased to about 234.48% during the last 73 years.

Introduction of Global Positioning System opened up a

new frontier in surveying, with unprecedented accuracy especiallyin this terrain which had to be mapped to investigate fluvio-geomorphological processes so that such spatial database mayassist in adopting necessary reclamation schemes. GPS surveycarried out during 2000-2001, brought about exact extent ofactual present area under badlands, shape and length of theescarpments, rate of gully headwall retreat, location of micro andmeso scale geomorphic features, gully networks etc. The GPShardware and software used in the survey (Trimble TDC 1 andTCS-1 receiver with Pro XR antenna and Pathfinder Office V 8.2software) were capable of providing sub meter accuracy afterpost processing of the collected data. Universal TransverseMercator (UTM Zone North - 45) projections was used in thestudy as this was found to be the most convenient projectionsystem for transferring the GPS-generated vectors directly toGeomatica V8.2, the RS/GIS software used for mapping. EVOLUTION OF GARHBETA BADLANDS IN MEDINIPUR DISTRICT OF WEST BENGAL Initially this area was a flat-topped lateritic upland.Shifting of river Silai towards the upland and erosion along itsconcave bank produced a steep escarpment (>20m) revealing 4to 5 distinct indurated horizons. Gullies dissected the duricrustedsurface and extended headward resulting in rapid scarp retreat.Four stages of Gully development at Garhbeta Badland: Stage

Process

Location

Loosening of soils by raindrop erosion & initiation of small

ephemeral channels known as rills.

In the southern periphery of the lateritic upland of the

whole badland sector of Garhbeta, where the general gradientof the terrain lies be

low 3°. f # -I

Upstream movement of the gully head & enlargement of

the gully in width and depth. The gully cuts to the horizon andthe weak parent material is rapidly removed. A waterfall oftendevelops where the flow plunges from the upstream segment tothe eroded channel below.

Over the bare and undulating lateritic escarpment surface

where medium gullies (G3) have established and the surfacegradient lies below 10°.

Healing stage with vegetation beginning to grow in the

channel. Established specially in the western part of the badlandwhere medium deep gullies have dissected the upland.

Stabilisation of the gully head, the channel reaches a

stable slope and the vegetation begins to grow in sufficientabundance to anchor the soil and permit development of newtopsoil. The healing stage is a necessary primed to stabilisationand the one stage grades into the other.

This stage of gully development can be seen in the

eastern part of the badland sector where matured gullies havesmooth gradient.

The badland of Garhbeta have two distinct parts viz. the

less mature Southwestern part (about 0.40 km2) & more matureNorth-Eastern part (about 0.85 km2). The maximum retreat ofthe gully head was found to be about 60cm/year. DEFINITION AND CHARACTERISTICS OF BADLAND 'Badlands', as the name implies, are barren areas of little or no economic value; generally devoid of vegetation and oftenhaving an extremely rugged terrain, which makeshuman access difficult; they are generally regardedas useless lands. The term can be traced to earlysettlers in western North America where scatteredareas of badlands are widely distributed. (Campbell1989) Encyclopedia of Geomorphology by R. W.Fairbridge describes badlands as extremelydissected landscape difficult to cross on horsebackand agriculturally useless. FrenchGeomorphologists define badlands as areasdissected by very fine drainage networks and shortsteep slopes with narrow interfluves. The slopesmay terminate abruptly in pediments on a miniaturescale and are often completely free of vegetation.

RAINSPLASH EROSION It occurs when raindrops fall [raindrop fall at914 cm/s (30ft/s)) on unprotected ground. Whenraindrop strikes the ground surface the soil particlesbecome more loose and splash due to impact force.A momentary building up of the pressure gradientstowards the edges of the drop disintegrates the soiland shoots some particles out. The slashed particlesreach to heights ranging up to 2-5cm and horizontallyupto an average of 5cm depending on their size andslope of the ground at Garhbeta. The importantinfluencing factors of rain splash are the mass andvelocity of raindrop and the soil character.

SHEET EROSION

At lateritic Garhbeta badland region sheet

erosion result significant surface wash over theundulating upland surface upto the gully head duringhigh intensity precipitation events. The westernsection is much bare that results tremendous sheetflow and surface removal. Whereas the eastern gullysection though the gully channels have more widthand length, the upland surface is less undulating andgradient averages to 2°-5°. Here the sheet oroverland flow becomes active when sufficient rainfalloccurs (100 mm/hr). The surface particles are alsolittle smaller (<3mm) compare to western gully sector,which results high ground water percolation andsteady overland flow especially when sufficient rainfalloccurs. RILL EROSION

Studies of hydraulic characteristics of the flow show

(ii) Overland flow with concentrated flow paths, (iii) Micro-

channels without head cut and (iv) Micro-channels with headcut.

The greatest differences exist between the 1st and 2nd

stage, suggesting that the flow concentration within the overland flow should strictly be treated as part of an incipient rill system (Merritt 1984). In the 2nd stage, small vortices appear in the flow, which, in the 3rd stage, develops into localised, spots of turbulent characterised by roll waves andW eddies.

II Based on the surface slope and velocity of flow the rill

channels on Garhbeta lateritic upland can be classified intom 1 three types :

(a) Small or minor rills, (b) Moderate rills, (c) Major or

developed rills.

GULLY EROSION Gullies are open erosion channels at least 30cm deep which conduct ephemeral runoff and are frequentlycharac remove vast amounts of soil. Removal of topsoil and subsoilterized by fast-flowing surface water creates abrupt deep and wideby gullies, of two different kinds: scouring gullies andsteep headward erosion. In scouring gulling, run-off watersidew concentrated in rills or depressions removes soil particles.alls Material commonly moved is the size of fine to medium sandand aor may be derived from slaking, when large aggregateslack ofdisintegrate upon wetting. Scouring is often associated withvegeta gently undulating landscapes.tion. THE CAUSE & PROCESSESGulliestend to OF LINEAR EROSION (i.e.becom Rills & Gullies) INedeepe GARHBETAr withThe cause of linear erosion is to be sought in runoff energy,succe which depends on runoff volume and its squared speed.ssive 3 THEORIES OF THE ONSET OF RUNOFFflowsof 1. Horton's theory (1945): Runoff starts when rainfall intensitywater exceeds soil absorption capacity. Comparing infiltration toand rainfall intensity,! absorptioncan decreases over time partly because capillary potential falls as the wetting front penetrates into the soil, and partly because soil structure at the surface was deteriorated.

2. Soil saturation theory: Runoff starts when all the pores in the soil are filled with water. In the cause of a simulated rainstorm, if runoff starts after rain has soaked the soil, it will increase until it stabilizes at a level corresponding to the absorption capacity of the soil. However if the rainfall persists (runoff may rise again, reaching a new plateau of stabilized infiltration. This simply means that the tilled horizon has reached saturation, so that the macroporous storage capacity of this horizon is filled to overflowing. If the underlying horizon is totally impervious, the amount of runoff will correspond precisely to that of the simulated rainfall; there may, however be a corresponding to that of the plough pour. When the soil is totally saturated, any drop of rain will runoff respective of rainfall intensity.

measured at the river-level depends on the area of the saturated soil in the valley bottom. If watershed surface runoff is measured during the dry season, it is seen that the river reacts very quickly to rain storms whereas no runoff is seen on the slopes! The volume of is less during this dry period because only a narrow ship in the valley bottom is saturated - often only the minor bed. At the end of the winter, however, when the whole soil cover has been soaked to capacity, the slightest rainfall replenishes the aquifer, which will spread out sideways, saturating a greater areas of the valley. As a result, even if there is no runoff on the slope during the rainy season, the entire watershed well contribute to the volume of flow in the river through extension of the saturated area, in as much as the ground water is recharged directly by draining the entire basin.

The stages of weathering and erosion observed in the region are:

1. The Preparatory Stage

During this stage the surface is prepared for sculpturing. Based on seasonalcharacteristics of climate such preparatory stage can classified into winter andsummer conditions.1a. Surface preparation during winter condition (December -February) : Just after the monsoon the surface moisture isreduced gradually due to lowering of atmospheric humidity.Significant fluctuation of diurnal, temperature about 18° -20°C, isfound which results destru :tion of seasonal vegetation mainlygrasses at different stages of the badland sector of Garhbeta.During December and January when the minimum temperaturefurther goes down below 9°C and atmospheric moisture goesdown below 65% the surface of the terrain become very dry andloose and numerous cracks and joints progresses with surfacecontraction over the lateritic upland.

The depth to ground water level in the phreatic zone gets

low in winter months and varies between 1.5m to 9metres belowland surface. The winter season persists upto February andbefore onset of summer a transitional period occurs for about 15 -20 days.

1b. Surface preparation during summer condition (March - May):

During summer the atmospheric temperature at daytime atGarhbeta increases up to 45°C. However, at night, thetemperature goes down to 25°C. This fluctuation encouragessignificant processes of mechanical weathering. The bare darkcolored and granular surface of the lateritic upland of Garhbetamakes suitable conditions for weathering processes to bemaintained. Occasional occurrences of thunderstorms (locallycalled Kalbaisakhi) transport loose and unconsolidated surfacematerials, which are afterwards washed out more easily by thesurface runoff or sheet wash.

From middle of May up to the 2nd week of June, the

groundwater regime further goes down from 2.8 to 18.0 metresbelow land surface. This lowering of groundwater also hassignificant impact of laterisation process and surface wash after aprolonged dry season. Therefore, in the preparatory stage theseasonal and diurnal fluctuation of air and surface temperaturealong with the fluctuating groundwater make suitablepreconditions for fluvial erosion with formation of rills and gulliesduring the rainy season.

2. Surface erosion stage / Processing stage

The surface erosion stage at Garhbeta starts from middle of

June at the onset of monsoon rains. The factors that influencessoil erosion by water is the mean annual rainfall and rainfallintensity. Severe erosion in the badland sector of Garhbeta isassociated and accentuated with high mean annual rainfall(about 1400mm and poor growth of vegetation). v^TIER GULLY DEVELOPMENT

As observed by Bandyopadhyay (1988), a distinct 3-tier

gully development, genetically unrelated to each often, is seenin the region. Numerous but small (depth : 1-2m) gullies underthe first tier develop above the escarpment, etched on the topmost laterite hardcap. 4 to 5 gullies of the first tier open out into asingle gully of the 2nd tier (depth : 10 - 15m) that extendsheadward with basal sapping 3-10m below the top levelduricrust & with the consequent retreat of the escarpment. Thematerial deposited by the 2nd tier gullies in the erosional plaincreated by the retreating escarpment are found to be dissectedby the gullies of the 3rd tier (depth : 0.5 - 1m) which are

Types and Number of Gully Channels at Garhbeta badland (Eastern Sector)

General Classification of gully channels at

Garhbeta badland SpecificatioNo. Name Type Depth Sid Width (m) (m) slope1 Very small gullies Gi <1.5 <10.0 <82 Small gullies G2 1.5-3.0 10.0-15.0 8-153 Medium gullies G3 3.0-9.0 15.0-18.0 15-454 Deep & narrow gullies G4 >9.0 >18.0 >45 SHAPE OF GULLIES The riverine gullies of Garhbeta area are characterizedby three common morphological features e.g. gully-head,gullyneck and gully body. The morphometric properties of asample gully draining into the Silai river include 'notched shape'of gully head with a maximum width of 3.9m and constrictedsection of 2.0m width, narrow gully neck of 2.5m thickness andelongated shape of gully body of 35m length. Besides a fewexceptions, almost all of the gullies are characterized by plungepools'. The longitudinal profile of an active gully denotes thepresence of gully heads, gully heads, gully neck, cliff face,plunge pools, and gully body on the basis of morphologicalcharacteristics the gully heads have been divided into four typesviz. (i) pointed gully head (ii) circular gully head (iii) notchedgully head and (iv) digitate gully head.

The gullies of Garhbeta area vary significantly as regards

their shapes and morphological characteristics and thus theyhave been classified into six types e.g. (i) linear gullies (ii) parallelgullies (iii) gullies (iv) bulbous gullies (v) rectangular gullies and(vi) mixed gullies represents different morphometric properties ofsample gullies. Linear gullies are long (13.9m to 60m) withpointed narrow gully heads (ranging in length from 2.2m to 2.6m).Sometimes, a few very small tributary rills also develop on eitherside of the main gully body. It may be pointed out that lineargullies no longer always remain narrow because their valleys arebroadened and are transformed into bulbous, trellis or mixedtypes. They generally develop in the area having highestconcentration of surface run-off through a single channel. Theyundergo the fastest rate of advancement through headwarderosion. In a single rainy season, the extension of linear gulliesranges from 10m to 20m Parallel gullies, which represent group oflinear gullies, have developed on concave side of the Siiai river atGarhbeta. Trellis gullies have developed on moderately slopingground with multiple channel flow of accelerated surface run off. Itis evident that trellis pattern of gullies is characterized by longestlength of gully heads (10m to 28m) and greater depths (8.1m to15m).

Bulbous gullies have developed in areas having moderate

flow of surface run off with maximum exhumation of solubleminerals from A horizon of the soil profile B, and B horizons.Semicircular or amphitheatre like heads of bulbous gulliesgenerally develop due to buckling down of A horizon fostered byexcessive mudflowy/

through B horizons. Rectangular gullies have very poorly

developed in the study area.

MORPHOLOGICAL CHARACTERISTICS OF SAMPLE

GULLIES

DETERMINATION OF SHAPE OF MACRO GULLY INS WESTERN SECTOR AT GARHBETA Shape of macro gully in western sector of Garhbeta have been determined from which idea of gully head, gully floor and gully side walls can be done. Through the determination of gully shape the

^/WESTERN AND EASTERN GULLY

As seen before, the badlands of Garhbeta can be classified as western (or less matured) and eastern (or matured) parts. In the western part, gullies are short and discontinuous, slope of the gully wall is between 60-90°; their height varies between 18-25m. Whereas in the eastern part, gullies have greater length; slope is gentle and convex (5-45); height of the gully wall is below 15m. Our observation shows the orientations of the gullies are very much integrated with nature and properties of laterite profile. The profile shows, there are 4-5 distinct horizons and due to differential sedimentary composition each profile has differential resistance to erosion. As a result gullies in Ganganir Danga occur in different levels. One set of gully drain the surface of the lateritic duricrust and the other cut into the lower horizons originating from the retreating cliff line.

Distinct characteristic difference can be seen between eastern and

western gully channels. V-shaped gullies form in material that is equally or increasingly resistant to erosion with depth. U-shaped gullies form in material that is equally or decreasingly resistant to erosion with depth. As the substratum is washed away, the overlying material loses its support and falls into the gully to be washed away. Most V-shaped gullies become modified toward a U shape once the channel stabilizes and the banks start to spell and slump.

\/CONG PROFILE OF GULLIES

Long profile is the section or line which can be obtained by plotting the axial line of the channel from source to mouth. As gully slopes arecommonly steep in the headward sides and gentle in the lower reachesprofiles are normally concave upwards.

Here Macro, Meso and Micro types of longitudinal profiles are

determined by the use of clinometer, Abney level and prismatic compass.While determining the longitudinal profiles an idea can be done of the slopeof longitudinal profile. For e.g.,cliff slopes are found on escarpment faces. Cliffs are so steep (40° or more)that the products of weathering for the most part fall immediately to the base.There is little or no accumulation of detritus on the cliff itself and it is thereforecommonly and meaningfully referred to by geomorphologists as a free-face.

Scree slopes are also found which varies from 35° or more in thelongitudinal profile. Aggradational slopes are seen in the longitudinal profile. Itvaries from 20° -35°. Eventually the cliff may disappear entirely to be replacedby a wholly aggradatinal slope at 20° - 35°. In its lower part, a longitudinalprofile will commonly exhibit a concave section. Rectilinear slope profile isoften observed in the Garhbeta badland area which is straight in profile.

MICRO RELIEF FEATURES IN GARHBETA

On the basis of survey by dumpy level and prismatic compass relief featuresare obtained for a gully catchment area. Through this survey in a catchmentarea it is found that high relief is found in the Eastern and Southern part.Based on this variation of relief features serial profiles are drawn and they aresuperimposed to identify the micro relief features of the gully catchment area.

Some useful data on Garhbeta badland:

SI Parameters Quantifi1 Present total area covered by 3 badlands2 Area occupied by Eastern gully sector Western gully sector3 Average extension of area under badlands (for the 56. last 8 years)4 Total length of escarpment Role of escarpment retreat Maximum 8 Average 10-15 Height of the escarpment Maximum Average6 Average slope of the terrain7 Area affected be sheet 14%erosion 8 Area affected by rill erosion 9 Area affected by gully 72% of total erosion 10 Linear extension of rill Maximum channels Average 11 Linear / headward extention of Maximum gully channels Minimum Average 12 Gully channel morphology Slide slope Maximum Average Depth Maximum Average Width Maximum Average Length Maximum Average

IMPACTS The impact of Gully Erosion are -

(i) Gully erosion means the loss of large volumes of soil.

(ii) Deep wide gullies, sometimes reaching 30m deep, severely limit the use of the land. (t«) Off-site deposition of soil causes water-qualify decline in streams or rivers. (iv) Large gullies disrupt normal form operations, creating access problems for vehicles and stock.(v) Low soil organic matter levels, lower fertility levels, changes in soil pH, exposed subsoil and parent material discourage crop production in gullies and rills.(vi) Soil erosion in the badlands of Garhbeta has seriousimpact on the surrounding environment by decreasing soil fertilityand land productivity. It also reduces the capacity of soil to absorbrainfall that often results in increased flooding and reducedground-water recharge, augmenting sediment loads in rivers andstreams. This degrades the quality of water supplied downstreamand cause silting of channels and reservoirs, in turn, increasingrisks of flooding and reduction in dry* season water supply. Suchan area was selected by us for study, because all stages of watererosion, channel initialization, rill and gully development slopeevolution, and other land sculpturing activities are found in thisrather meso-scale topographic unit. Geomorphologicalinvestigation of water erosion on land sculpturing, role of fluvialaction on a specific land and significance of climatic variables ondevelopment of badland topography. The badland though coversa small area, is a natural plot in itself for carrying out fluviogeomorphological investigations and research through real timemonitoring techniques.